1. Field of the Invention
The present invention relates to a hydrotreatment process for sulfur, asphaltene and metal removal from petroleum residuals and other carbonaceous materials. In one of its more particular aspects, this invention relates to a process in which desulfurizing, deasphalting and demetallizing reactions occur simultaneously in a reaction zone comprising molten potassium hydroxide and water. In another aspect this invention relates to such a process wherein the potassium hydroxide spent in the hydrotreating reactions is regenerated for reuse in the hydrotreatment process.
2. Prior Art
The steadily increasing demand for distillate petroleum products and the availability of low grade carbonaceous feedstocks such as heavy petroleum residuals, provide incentives for the development of processes for upgrading such feedstocks, which usually contain sulfur, oxygen, and nitrogen as well as various organometallic compounds.
One method of upgrading low grade carbonaceous materials is desulfurization. U.S. Pat. No. 3,164,545, for example, discloses a desulfurization process in which a petroleum fraction is contacted with a molten alkali metal hydroxide containing 5-30% water at a temperature of about 300.degree.-900.degree. F. (150.degree.-480.degree. C.). However, this process merely removes some of the sulfur and other impurities from carbonaceous feedstocks without otherwise improving the quality of such feedstocks.
Another suggested process for beneficiating carbonaceous feedstocks is hydrocracking, which is a decomposition at high pressures and elevated temperatures, with the addition of hydrogen and usually in the presence of a catalyst, such as zeolite, with a platinum, tungsten oxide, cobalt-molybdenum oxide or nickel component. These catalysts may be altered by promotion with another metal or by a pretreatment such as sulfiding. Under these conditions, hydrogenation occurs simultaneously with cracking. Thus, the buildup of tar or coke on the catalyst surface is substantially minimized. A number of problems are involved in these processes, however, including catalyst deterioration caused by the sulfur, nitrogen or ash in the feedstock, presence of hydrogen sulfide in the products and catalyst deactivation resulting from coke and ash deposition on the catalyst surfaces.
It has been proposed that many of these disadvantages can be overcome by a hydrocracking process employing a molten salt as a catalyst. It has been suggested, for example, to use molten zinc chloride or zinc chloride mixed with a zinc oxide acceptor. The use of such molten salt catalyst obviates many problems of the prior art. The catalyst in the form of a molten salt offers a number of advantages, including excellent heat transfer characteristics and continual renewal of fresh catalyst surfaces. In addition, contaminants such as catalyst poisons can be withdrawn with a bleed stream of the molten salt to allow uninterrupted operation. The use of zinc chloride is not without problems, however, since zinc chloride is highly corrosive at elevated temperatures. Further, the solubility of the heavy hydrocarbons in molten zinc chloride is high and makes separation of the organic and salt phases difficult.
In U.S. Pat. Nos. 3,677,932 and 3,736,250 it is suggested that the solubility of hydrocarbons in molten zinc halide may be substantially reduced by the addition thereto of certain alkali metal halides. These processes are not altogether satisfactory, however, because separation of the hydrocarbon products from the salts is incomplete. Further, the regeneration of such mixed salts is a complex procedure requiring high-temperature treatment in a corrosive atmosphere.
In U.S. Pat. No. 3,745,109 there is disclosed a hydrocarbon conversion process in which hydrocarbons such as partially refined petroleum are contacted with a sulfide containing alkali metal carbonate melt. In the presence of hydrogen and at appropriate temperature and pressure conditions, the partially refined petroleum is hydrocracked. This process, although obviating many of the problems of the prior art zinc chloride processes, still is not altogether satisfactory. More particularly, the yields obtainable are lower than is desirable. A commercially viable hydrocracking process should provide a conversion of at least 75-80% of the feedstock. Further, at least about 60% by weight of the product should be obtained as a normally liquid product substantially free of sulfur and metallic ash constituents, such that it is suitable for use as a feed material to a conventional petroleum refinery.
U.S. Pat. No. 3,846,275 suggests a coal liquefaction process which comprises contacting a solid carbonaceous material with a reducing gas, water, and a catalytic compound containing a sulfur component and an alkali metal or ammonium ion at liquefaction conditions to produce a mixture comprising an aqueous phase and a hydrocarbonaceous phase which are separated. The hydrocarbonaceous phase then is extracted with a hydrocarbonaceous solvent to provide an extract fraction, from which the liquefaction product is recovered, and a solid residual fraction.
A similar process is disclosed in U.S. Pat. No. 3,796,650. The suggested process comprises contacting coal with water, at least a portion of which is in a liquid phase, a reducing gas, and a compound selected from ammonia and carbonates and hydroxides of alkali metals, at liquefaction conditions including a temperature of 200.degree.-370.degree. C. to provide a hydrocarbonaceous product. It is a disadvantage of both foregoing processes that the yield of liquid product and amount of feed material converted are less than desirable. In addition, such processes require an aqueous phase reaction. The high temperatures necessarily result in a requirement for excessively high pressures to maintain the aqueous phase.
Another such aqueous process is disclosed in U.S. Pat. No. 3,642,607 wherein a mixture of coal, a hydrogen donor oil, carbon monoxide, water, and an alkali metal hydroxide are heated to a temperature of about 400.degree.-450.degree. C. and under a total pressure of at least about 4000 psig to obtain dissolution of the coal. However, this process suffers from the same disadvantages as the other aforementioned aqueous processes.
U.S. Pat. No. 4,003,823 discloses a process for desulfurization and hydroconversion in the presence of a desulfurizing agent comprising an alkali metal hydroxide. A reaction zone is maintained at a pressure of about 500-5000 psig and a temperature of about 700.degree.-1500.degree. F. (371.degree.-816.degree. C.). The product is a desulfurized, demetallized, and upgraded heavy hydrocarbon feedstock with about 50% of the sulfur being removed by the process. Although providing some advantages, this process suffers from the drawback that substantial amounts of gas and char form during the process.
U.S. Pat. No. 4,092,236 discloses a process for converting coal to cracked products including a major amount of liquid and a minor amount of gaseous and solid products of enriched hydrogen content utilizing a molten salt bath comprising an alkali metal hydroxide, preferably sodium hydroxide. Preferred conditions are a temperature of about 400.degree.-500.degree. C. and a pressure of 50 to 300 atmospheres. Although this process is capable of hydrocracking coal and producing a product mix which has desirable characteristics, the product still contains about 2-10 wt. % of normally gaseous hydrocarbons and 5-30 wt. % of solid hydrocarbonaceous products.
The removal of metals from petroleum products is another method of petroleum residual beneficiation which has been explored. The two most common metals in petroleum crudes and residuals, vanadium and nickel, occur principally in porphyrinic and other organic structures. In crudes which are high in metals content, the vanadium concentration may reach 0.2% and the nickel concentration 0.01%.
U.S. Pat. No. 2,383,972 discloses a process for recovering vanadium from petroleum during the course of a cracking operation which comprises reacting the metallic constituents of petroleum oil, including vanadium, with a solid hydrated sodium aluminum silicate of the zeolite type. Vanadium is recovered from the zeolite by means of solvent treating the zeolite with a strong mineral acid, precipitating the vanadium as ammonium vanadate, roasting the ammonium vanadate to produce the oxide, and reducing the oxide in an electric furnace.
U.S. Pat. No. 2,789,081 discloses a process for the refining of mineral oil which comprises contacting heavy lubricant obtained in a vapor phase refining process with bauxite to remove principally alkali metal contaminants.
U.S. Pat. No. 2,990,365 discloses a process for demetallizing hydrocarbon oils by modifying the properties of complex organometallic compounds, including vanadium organometallics occurring in the oils, by contacting the hydrocarbon oils in the liquid phase with a fused alkali metal hydroxide. The organometallic compounds present are thereby converted to alkali metal salts, which have greater water solubility and can be more easily removed from the hydrocarbon oils than the organometallic compounds.
U.S. Pat. No. 3,936,371 discloses a process for the removal of metal contaminants from heavy hydrocarbon oils by means of treatment with "red mud", a residue which occurs when bauxite is dissolved at high temperatures to provide alumina as a raw material for the electrolytic production of aluminum. Contacting the hydrocarbon oil with the "red mud" at temperatures in the range of about 350.degree.-500.degree. C. in the presence of hydrogen at a pressure of about 1 to 300 atmospheres is said to be highly effective in removing vanadium and other contaminants from the hydrocarbon oil.
U.S. Pat. No. 4,119,528 discloses a process in which simultaneous desulfurization, demetallization and hydroconversion of heavy carbonaceous feeds is accomplished by treatment with potassium sulfide and hydrogen. The process is carried out at a temperature in the range of about 700.degree.-1500.degree. F. (371.degree.-815.degree. C.) and a hydrogen pressure of about 500-5000 psig, but desulfurization is limited.